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The Jour. Myan. Acad. Arts & Sc 2004 VoL II(Part One) No. 2 (Science)

Study on Physical Properties and Chemical Composition of Some Gems

Kyaw Myint Htoo, Tun Khin& Sein Htoon

Abstract

Physical properties of some Myanmar gems were studied by using refractometer, dichroscope, polariscope, SG test, UV test and microscope. Then .chemical composition were investigated by XRF - technique. After that, gem identification, evaluation, colour improvement were studied according to these physical properties and chemical composition.

Keywords: physical properties, chemical composition, XRF technique

Introduction

The study of gems through science which includes the formation of gem stone, properties, identification, grading and evaluation are called gemology. Myanmar gems can be divided into precious stone: , , , , , and other precious stone: , , , , aquamarine, , zircon, , , apatite, danburite, moonstone, iolite, , citrine, scapolite, ...etc.. A gem stone is a material that has intrinsic value and posses three fundamental quality (1) beauty (2)durability (3)rarity. Colour contributes to the beauty of gem, major factor for grading and evaluation and also an important properties for identification. Gems are some kind of and a most important characteristic of a is the possession of structurally homogeneous solid of definite chemical composition formed by the inorganic process of nature. Most minerals occur as crystals and it must have systematic structure and it must be natural product. We can

Department of Physics, University of Yangon 174 The Jour. Myatu Acad. Arts &. Sc 2004 Vol. II (Part One) No. 2 (Science) study the gems according to the chemical composition and physical properties such as , coloiir, , double refraction (), doubling of back facet edges, dichroism and pleochroism, absorption spectrum, specific gravity, hardness, luster, or fire, and phosphorescence.

Experimental

This research work was done at universitie's research centre and gem laboratory, geology department, YU. The physical properties of some Myanmar gem were studied by using refractometer, dichroscope, polariscope, chelsea colour filter, ultra-violet light, specific gravity test, hand len and microscope. Laboratory technique in gemology are x - ray method: radiographic technique, x- ray diffraction technique; spectrometric methods: infra-red spectrometer, uv- spectrometer; thermal conductivity meter; reflectance meter and scanning electron microscopy. The FTIR spectrophotometer test is a practical and effective method for detecting most type B jadeite which after acid bleaching are impregnated with resin to fill up cracks and to improve transparency. Accurate scientific tests will safeguard consumers as well as the industry. So far, spectrophotometry is the single most reliable non-destructive test for identifying, type B jadeite Then, the chemical composition of some Myanmar gems were, investigated by shimatsu ED700.

Result and discussion

We can identify gem quality according to physical properties: crystal system, colour, refractive index, double refraction, doubling of back facet edges, specific gravity, hardness, luster, dispersin, uv test and The Jour. Myan. Acad. Arts & Sc. 2004 Vol. II(Part One) No. 2 (Science) 175

inclusion. Inclusion are particle of solid, liquid or gaseous material enclosed within a . The nature of such inclusions provides a powerful clue to the origin of the stone, and enables natural stone to be distinguished from their synthetic counterparts.

Table 1. Physical properties of some Myanmar gems Gem Ruby Sapphire Spinel Peridot Jade Crystal Trigonal Trigonal Cubic Orthorhombic Monoclinic system

Colour Red Blue, Red, Orange, Yellow green White, Colourless Violet, etc Green, Pink RT 1.76-1.77 1.76-1.77 1.715 1.654-1.690 1.67 DR 0.008 0.008 0.036 DBF strong SG 3.99 3.99 3.58-3.61 3.34 3.33 HN 9 9 8 6 1/2 6.5-7 Laster Vitreous Vitreous Vitreous Vitreous Vitreous Dispersion 0.018 0.020 UV glow Faint glow Faint glow glow inert (long) Test inert inert inert inert inert ( short)

We can also identify roughly according to the major chemical composition.

Ruby and Sapphire - AI2O3 Peridot - (Mg,Fe)2Si04

Spinel - MgO.Al2O3 Jadeite - NaAl ( Si2O6 ) 176 The Jour. Myan. Acad. Arts & Sc 2004 Vol. II (Part One) No. 2 (Science)

Purest AI2O3 is colourless (white sapphire),with trace of Cr, colour changes to red, called Ruby. With trace of Fe and Ti, colour changes to blue, called Sapphire. The red colour Spinel contains higher content of C^Ch. Colourless Spinel contains major amount of AI2O3 and MgO. The orange colour contains higher content of V2O5 and bluish gray to deep purplish b lue c olour s pinel c ontains h igher c ontent o f F e2O3.lt w as also found that Zn rich sample becomes orange colour and Cr rich sample becomes red colour.

Table 2.'Chemical composition of some Myanmar gems

Ruby Ruby Element% Sapphire Spinel Peridot Jade (Mogok) (Mirgshu) AI2O3 91.453 83.469 90.779 71.3 25.529

Fe2O3 1.222 0.242 4.682 1.21 33.396 0.821

SO3 5.559 3.849 2.549

SiO2 12.461 36.912 54.216

Cr2O3 0.819 0.976 0.947 0.167 CaO 0.790 2.434 1.319 SrO 0.150

TiO2 0.215 0.401

ZrO2 0.137 MgO 10.32 27.039 ZrO 4.19

V2O5 0.169 1.216

CaO3 0.125 NiO 2.255 MnO 0.428

Na2O 11.113 The Jour. Myan. Acad. Arts & Sc 2004 Vol. II(Part One) No. 2 (Science) 177

Ultra-voilet test UV( long;) UV (short) Ruby (natural) glow inert Ruby (synthetic) glow glow(10 sec)phosphorescence Sapphire (natural) glow inert Sapphire (synthetic) glow greenish white glow Spinel (natural) inert inert Spinel (synthetic) glow faintglow

Conclusion

The experimental results indicate that the physical properties and chemical composition are very useful to identify and evaluate the gems. It is found that with instrument test are very useful and without instrument test are also. Every gem has specific gravity and RI, so we can easily identify according to these value. The overwhelming presence of enhanced gems has been a major worry for the industry. Known as type B jadeite, enhanced jade looks, feels and reacts to various chemical and chemical test much like natural jadeite. Ironically, type b jadeite has created a saturation in which natural jadeite is mistaken as type B jadeite, making consumer more leery of buying jade. Accurate scientific test will safeguard consumer as well as the industry. X- ray is very useful in the testing of gems and its simulates. The use of direct radiography relies on the fact that different materials have varying degrees of transparency to x- ray. This assists comparison of diamond and its substitute; diamond are transparent to x- ray, stimulant are not. It is also useful for detecting glass filling in gem. It is also used to examine the effect of diffraction of the ray from the atomic crystal structure planes of material. X- ray diffraction can be used to distinguish between natural and stimulants .X- ray are even more dangerous then light , and should never be used except qualified staff under laboratory condition. SEM uses an electron beam to scan the prepared surface of an object. Scattered electron reflections are detected at very high magnification. When you determine the gem stone, it is important to consider that whether the stone is natural 178 The Jour. MyamAcad. Arts & Sc. 2004 Vol. II(Part One) No. 2 (Science) or synthetic or enchanced? Is the colour natural or not? Are there any noticeable inclusion? Then, how can it be used material science in physics ?For example, quartz can be used as oscillator and tourmaline can be used in electronic instrument due to its pyroelectric, i. e. develops opposite electric charges at the two end of the crystal when it is heated. This research work study the chemical composition by using XRF technique and physical properties; SG, HN, colour, luster, crystal system, RI, DBR, DBF, dispersion by using laboratory instruments. According to the experimental results, we can say, such laboratory equipment are very powerful to study the identification, evaluation, colour improvement and provides the increase of their value of some Myanmar gem stones.

Acknowledgements

We wish to acknowledge with thanks to all staff of physics department, geology department, Yangon University and Universities' Research Centre for their kind helps to do this research work.

References

Kyaw Myint Htoo, Tun Khin and Sein Htoon. (2002) Investigation of concentration of elements contained in some Myanmar gems; in relation to their physical properties, school family day 2002

Kyaw Myint Htoo. (2002) Investigation of concentration of elements contained in some Myanmar gems; ruby, sapphire, spinel ,peridot and jade in relation to their physical properties. PhD Thesis.

Basic and Advanced Course on gemological class, Geology department, YU.